1. Field of the Invention
This invention relates to methods for isolating polymer resins from solution slurries utilizing a precipitation aid.
2. Brief Description of Related Art
A number of methods have been disclosed for separating soluble thermoplastic resins from organic solvents. A majority of these methods are energy intensive requiring the removal of the organic solvent. More energy efficient means involve the precipitation or coprecipitation of the polymer resin from solution. These precipitation techniques can be hindered by the presence of a solid phase of fine particulates within the solution. These fine particulates are not easily recovered before precipitation of the soluble polymer resin and can interfere with the recovery of the precipitate. The presence of this solid particulate phase is particularly troublesome when attempting to employ equipment which is not adapted to handle fine particles.
An example where this problem occurs is in the copolymerization of 2,6-xylenol and 2,3,6-trimethylphenol via oxidative coupling. It is reported that most of the copolymers formed from these monomers spontaneously precipitate in the reaction mixture as very fine particles. This reaction mixture turns into a three-phase slurry comprising: a solid phase of copolymer particles, a copolymer solution phase and an aqueous phase. In the preparation of polyphenylene ether homopolymers with 2,6-xylenol, the polymer reaction product remains solubilized in the toluene reaction solution. After purification of the solution, the homopolymer is typically precipitated in methanol. The polyphenylene ether homopolymer of 2,6-xylenol precipitates as large size clusters suitable for liquid-solid filtration. In contrast, the three-phase reaction mixture obtained with the preparation of polyphenylene ether copolymers of 2,6-xylenol and 2,3,6-trimethylphenol is unsuitable for the polymer purification and isolation techniques used for the polyphenylene ether homopolymers of 2,6-xylenol. Separate equipment is therefore required.
It is desirable to provide an isolation technique for polymer resins within a solution slurry that contains a solid phase of the polymer resin as fine particulates which does not require special equipment to remove these particulates.